Collision-Free Optimal Trajectory for a Controlled Floating Space Robot

Abstract

Space robots are key to the establishment of a new era of low-cost in-orbit operations. Given the complexities involved in designing and operating of a space robot, several challenges arise and developing new advanced methodologies for control and motion planning is essential. Finding an optimal trajectory for the space robot to attain an out-of-reach grasping point on the target or when the motion of the arm is restricted by singular configurations or obstacles, is a difficult task using the Degrees of Freedom (DoF) of the arm only. Hence, using the redundancy offered by the extra degrees of freedom of the spacecraft base to help the arm reach the target whilst avoiding singularities and obstacles is mission critical. In this paper, an optimal path planning algorithm using Genetic Algorithm was developed for a controlled-floating space robot that takes advantage of the controlled motion of the spacecraft base to safely reach the grasping point. This algorithm minimises several cost functions whilst satisfying constraints on the velocity. Moreover, the algorithm requires only the Cartesian location of the grasping point, to generate a path for the space robot without a priori knowledge of any desired path. The optimal trajectory is tracked using a nonlinear adaptive $H_{\infty }$ controller for the simultaneous motion of both the manipulator and the base spacecraft. The results presented prove the efficacy of the path planner and controller and it is based on a six DoF manipulator mounted to a a six DoF spacecraft base.